The present invention relates to a sound pickup apparatus for picking up a user's voice and a conference telephone equipped with the sound pickup apparatus, to enable establishment of a voice conference between remote locations.
A recently-developed sound pickup apparatus of microphone array type has a plurality of microphones and obtains a desired directivity pattern by subjecting signals output from the microphones to digital signal processing, and is built in various products.
A problem of such a microphone array is that it breaks down with a higher probability when compared with a sound pickup apparatus equipped with single microphone. JP-A-2002-159086 has been proposed as a countermeasure to the problem.
A summary of JP-A-2002-159086 will be described by reference to FIG. 19. The sound pickup apparatus has microphone units 12a to 12d. A failure diagnosis processing section 13 individually diagnoses a failure in each of the microphone units 12a to 12d. In accordance with a signal output from the failure diagnosis processing section 13, a normal microphone selection processing section 14 outputs only sound signals detected by the microphone units 12a to 12d that have been diagnosed as being normal. Subsequently, the voice signals are delayed by delay processing sections 15a to 15d, and the thus-delayed signals are output after having undergone delay-and-sum processing performed by an addition processing section 16. Thereby, a processed, noise-eliminated signal is output from the addition processing section 16. From the above, the sound pickup apparatus is configured so as to stably operate as a sound detector.
In the meantime, a conference telephone is mentioned as an example product equipped with a sound pickup apparatus. As in JP-A-3-293846, a typical example product is a conference telephone includes a microphone that converts audible sound into an electric signal, a loud speaker that converts the electric signal into audible sound, and a sound communications network that electrically connects the microphone and the loud speaker to a telephone line. The microphone has a directivity pattern in which a sensitivity of a sound emitted from at least one direction is greater than that of sounds emitted from the other directions. The reason why the sound pickup apparatus built in the conference telephone is imparted with such a directivity pattern is to reduce an acoustic echo which will be caused as a result of received voice reproduced by a speaker re-entering the microphone and being transmitted to a party on the other end. The acoustic echo itself is unpleasant and impairs call quality. In addition, when the acoustic echo is extremely large, howling may occur, to thus disable the call.
However, when a conference telephone is equipped with a microphone array for the purpose of reducing the acoustic echo, individually disconnecting a signal output from a broken microphone under the technique described in JP-A-2002-159086 may lead to output of an insufficiently-canceled signal component of the acoustic echo, which may in turn result in an increase in the acoustic echo.